Effect of number of turbine impellers on surface aeration in laboratory fermentor

Abstract

The effect of one and two four-flat-bladed turbine impellers on the surface aeration intensity in a laboratory tormentor was investigated at different agitation speeds and sparge rates. The surface aeration was found to be generally more intensive with two impellers for the same other operating conditions because of higher power consumption and the position of the upper impeller closer to the free liquid surface. The surface aeration intensity was successfully correlated in terms of power consumption and sparge rate. The aeration number alone cannot be used for general predicting surface aeration intensities.

Design of stirred vessels with gas entrained from free liquid surface

“…For unsparged vessels, Matsumura et al (1982a) have Veljkovic and Skala (1989) have shown that, QsA a Ph5 Q, Veljkovic et al (1991) Rushton Turbine From the above comparison, it can be seen that there is a large discrepancy between the various authors even about the dependancy of the effect of impeller speed and the impeller diameter on the rate of surface aeration. The rate of surface aeration, QsA a N1.9 lo s, and QsA 0: D4 7.…”

“…A similar technique for the measurement of the rate of surface aeration was used by Topiwala (1972), Veljkovic and Skala (1989) and Veljkovic et al (1991). Matsumura et al (1982a) have measured the rate of absorption by surface aeration for unsparged vessels.…”

“…In order to model the intensity of surface aeration in terms of the gas entrainment rate or the fractional gas hold-up, the Albal et al (1983) rate of surface aeration increases as the number of impellers is increased Veljkovic and Skala (1989) Baffles at high Froude number, the presence of baffles increases the mass transfer coefficient, the power consumption also increases Andou et al (1972) …”

“…A wide variety of impellers can cause surface aeration, for example, flat and pitched bladed Turbines (Calderbank, 1958(Calderbank, , 1959Blakebrough et al, 1961;Dierendonck et al, 1971;Brauer and Schmidt Traub, 1973;Greaves and Kobbacy, 1981;Heywood et al, 1986;Tanaka et al, 1986;Ram Mohan, 1987;Kolte, 1988;Veljkovic and Skala, 1989;Veljkovic et al, 1991), vaned disc turbines (Ram Mohan, 1987;Kolte, 1988), paddles (Miller, 1974), propellerpitched turbine combination (Matsumura et al, 1982a;1982b), conical impellers (Ram Mohan, 1987;Kolte, 1988), cone aerator (Nestmann 1983). Disc turbines, vaned disc turbines, pitched blade turbines, paddles, are shown schematically in Figure 2.…”

“…Equation (1 6) Thus the rate of surface aeration can be easily calculated by measuring the concentration of the dissolved oxygen at steady state and the volumetric flow rate of the gas sparged at the bottom and at the head space. A similar technique for the measurement of the rate of surface aeration was used by Topiwala (1972), Veljkovic and Skala (1989) and Veljkovic et al (1991). Matsumura et al (1982a) have measured the rate of absorption by surface aeration for unsparged vessels.…”